Using Midnite Brat to charge 12v batt from 24v Battery?

Got oddball need to keep a 12v battery hot from my 24 volt solar/ battery bank.PWM Brat would be fine as I have a steady 24 v source. Manuals on MidNite site do not make it clear if I can charge 12 from this higher voltage source?

Other suggestions appreciated. Need at least 20 amp charging for 12 v Battery.The brat does 30, so it is attractive!